Purpose: The literature has shown great interest in open innovation (OI), and also discussed its degree of openness based on, for example, the number of parties involved. Less is known, however, about what makes OI processes work. The purpose of this paper is to describe and discuss the importance of trust in OI, and the paper specifically focusses on a start-up company’s OI processes with collaboration parties. The paper points out how a lack of trust antecedents may disable such OI processes.

Design/methodology/approach: The empirical part of the paper consists of a case study on a medicine technology start-up. Interviews and analyses of secondary sources made up the main data capturing methods. Each collaboration between the start-up and another party is analysed through three trust antecedents: contractual, competence based, and goodwill.

Findings: The paper shows how either party may have chosen to discontinue the collaboration, based on the lack of competence or goodwill antecedents to trust. Specifically, the case indicates how the start-up discontinues the collaboration based on a perceived lack of goodwill, while the collaboration party bases its decision on competence deficits by the start-up.

Originality/value: The paper contributes to previous research through describing OI related to start-ups, and introducing trust antecedents as prerequisites for OI. To the literature on trust, trust mutuality makes a research contribution.